Infuse tarragon in a little water or stock for a couple of hours
Reserve some fresh leaves for garnish
Use 4-5 parts black (bilberry,blueberry or blackcurrant....not tried blackberry ....yet) to 1 or 2 parts navy rum
If using fruit strain the pips etc out by passing through a chinois (fine sieve)
Add wine vinegar (sherry raspberry or similar to taste)
Some cayenne as above
Reduce down, if too watery add some molases or soft brown sugar